People's proud invention of gears was preceded by mindless evolution: The tiny points on the legs of juvenile planthopper insects move like intermeshing cogs.

Those cogs in young Issus coleoptratus planthoppers touch at the upper parts of the legs, says neurobiologist Malcolm Burrows of the University of Cambridge in England. And when the planthopper leaps, gear teeth on one leg catch the teeth on the other in sequence. Meshing cogs get legs quickly moving in sync, enabling ener...